1. Field of the Invention
The present invention relates to a flow rate regulator used for a liquid or blood transfusion unit to regulate a flow rate of liquid medicine or blood flowing therethrough. Further, the present invention relates to a liquid medicine or blood transfusion unit having the flow rate regulator used therefor.
2. Description of the Related Art
When a medical instrument such as a liquid medicine applicator, a blood transfusion unit or the like is used, it is necessary to regulate the flow rate of the liquid medicine or blood flowing through a tube. To this end, it is well known that a flow rate regulating device is disposed midway of the tube.
Many kinds of flow rate regulating devices have been heretofore known. Among the many conventional simple and inexpensive flow rate regulating devices, a typical one is designed in the form of a roller clamp. The roller clamp is constructed by a housing and a roller rotatably accommodated in the housing. A tube through which liquid medicine or blood flows is clamped between the housing having a suitable angle of inclination and the outer peripheral surface of the roller. Accordingly, the flow rate of the liquid medicine or blood is regulated, as required, by properly varying the degree of clamping by displacing the roller toward or away from the housing.
With the above described roller clamp, it has been found that the throat portion of a tube is deformed as time elapses, causing the flow rate to be reduced gradually due to gradual reduction of the effective cross-sectional area of the tube. To obviate the foregoing problem, several improvements have been tried. One of the improvements which has been put in practical use, involves a roller clamp including a housing having a bottom which is formed with V-shaped grooves. However, this improved roller clamp suffers from the problem that the flow rate varies under the influence of temperature variations, although variation of the flow rate over time has been reduced remarkably when the improved roller clamp is used at a constant temperature.
In addition to the aforementioned roller clamps conventional flow rate regulating devices are disclosed in, for example, U.S. Pat. Nos. 3,877,428, 4,428,397 and 4,769,012 and Japanese Laid-Open Patent No. 247,470/1986. Each one of the conventional flow rate regulating devices is constructed by combining and assembling a plurality of components together so as to allow the flow rate to be regulated by varying the cross-sectional area of the flowing passage. The respective flow rate regulating devices disclosed in the prior U.S. patents have drawbacks in that they are complicated in structure and require a plurality of split molding dies for molding the components, resulting in high manufacturing cost, particularly driven by increased expenditure required for the molding dies. On the other hand, the conventional flow rate regulating device disclosed in the Japanese laid open patent is constructed merely by two components. However, it has been found that this flow rate regulating device also has drawbacks in that it has a narrow range of flow rate regulation and it has a low flow rate accuracy. Accordingly, it can be concluded that all of the conventional flow rate regulating devices have limited practicability.